In recent years, along with the rapid development of pharmacological and biomedical science, medical biodegradable materials having excellent biocompatibility and biosafety are increasingly demanded internationally and domestically. The biodegradable PLA has been significantly applied in pharmacological and biomedical science, for example, it is used as the carrier for targeting drugs and controlled release drugs, hard tissue repair material and supporting material for biologically active species in biomedical engineering. By using PLA as the drug carrier, the medical effect can be largely improved, and the dosage and drug's side effects can be reduced. When PLA is used as the drug carrier, the polymer with the weight average molecular weight (Mw) 1.5×104˜3.0×104 is generally used (Zhao, Y.; Wang, Z.; Yang, F. J. Appl. Polym. Sci., 2005, 97, 195-200). However, such polymer should not contain any toxic metal and other toxic components. Currently, commercial PLA is produced mainly by the following two methods: 1. It is synthesized by using stannous octoate to catalyze lactide by ring-opening polymerization; and 2. It is synthesized by using stannous chloride to catalyze lactic acid by direct polycondensation. Although these two methods can be used to synthesize the required polymer, the catalyst tin salt cannot be completely removed from the polymer after polymerization reaction. Many researches have been conducted by foreign and Chinese scholars to prove that stannous octoate and stannous chloride have cytotoxicity. Consequently, scientists around the world start to question the safety of PLA that is synthesized by using stannous octoate and stannous chloride as the catalyst and which is used as the pharmaceutical carrier. The most important problem raised by worldwide biomedical material scientists to be solved is to use the high-effective and nontoxic catalyst to synthesize the medical PLA. At present, there are two methods using non-metal catalysts to synthesize the biodegradable PLA in terms of ring-opening polymerization: 1. Two-component catalysis. This method is developed by American scholar J. L. Hedrick et al. The principle is that a strong phosphine-amine nucleophilic reagent (e.g. triphenylphosphine, 4-dimethylaminopyridine, etc.) is used as the catalyst and alcohol (e.g. pyrenyl butanol, methanol, benzyl alcohol, etc.) as the initiator to prepare the PLA biodegradable polymer in terms of the ring-opening polymerization; and 2. Nontoxic and non-metal organic guanidine is used to synthesize the PLA. This method is firstly developed by Chinese scholar Li Hong (Distinguished Professor of School of the Environment, Nanjing University). The non-toxic and biomimetic organic guanidine (creatinine, creatine, glycocyamine, six alkyl acid guanidine, etc.) without metal and biomaterial is used as the mono-component catalyst to trigger the lactide activity to synthesize the PLA in terms of the controlled ring-opening polymerization. The direct polycondensation method used to synthesize the PLA is the one developed by Japanese scholar Y. Kimura by using stannous chloride to catalyze lactic acid. The advantage of such method is that lactic acid is directly used as the monomer (the ring-opening polymerization needs high purity of lactide made by lactic acid cyclic dimer as the monomer) and high-purity of monomer is not required, therefore, PLA production costs are largely reduced and it is possible for industrialization.